Repetition is a very fundamental factor affecting learning and memory. However, its beneficial effect increases to the extent that repetitions are separated by the occurrence of other informational units. Two functionally separable subphenomena are the "spacing effect" involving short spacings and the "lag effect" involving longer spacings. Understanding these spaced- repetition effects may help researchers understand why repetition benefits learning and memory in the first place. The present research addresses this problem from a developmental perspective. Preschool children do not exhibit a spacing effect in recall. It emerges with development between the ages of four and seven. However, in recognition, preschoolers do exhibit a spacing effect which is developmentally invariant over the next several years. This can be interpreted in terms of two-process theories of recognition in which both recognition and recall can be based on relational information in memory, and in which recognition also can be based on a relatively primitive form of item information. Experiments 1 and 2 address the hypothesis that, in preschoolers, spacing influences the encoding of item information but not relational information, whereas spacing influences the encoding of both kinds of information in older children. Experiments 3 - 7 are free recall studies designed to test several hypotheses about what developmental changes underlie the emergence of the spacing effect in recall. These hypotheses combine aspects of theories of the spacing effect (e.g., encoding variability or deficient- processing mechanisms) with hypotheses about the nature of developmental changes in memory (e.g., changes associated with elaborative encoding processes, degree of encoding variability, richness and accessibility of knowledge structures or the acquisition of voluntary encoding strategies). The lag effect in free recall seems to develop during early adolescence. Exp. 8 tests the hypothesis that the emergence of the lag effect is associated with the development of spontaneously-used organizational encoding strategies. In recognition, it is unclear whether developmental changes occur in the lag effect. To clarify this issue and determine the direction of future research, Experiment 9 assesses the lag effect (the effect of longer spacings) over a broad range of age groups.